The British & Irish Lions are facing an anxious wait as they determine the extent of the injury Sean O'Brien suffered on Friday.

O'Brien, who is equally adept at blindside and openside, injured his knee playing against Stade Francais in the Amlin Challenge Cup final. He will definitely miss Leinster's RaboDirect PRO12 final against Ulster this weekend and the Lions expect him to miss the first two or three matches on their tour of Australia.

If O'Brien's injury is more serious than first feared then it could see England's Chris Robshaw get the call up after he was omitted from Warren Gatland's original 37-man squad. But Gatland is optimistic the Ireland No.7 will be back fit sooner rather than later.

"He has some swelling and some bone bruising," Gatland said. "It will be a couple of weeks [before he is fit]. With bone bruising it's a little bit unpredictable. They said today it was probably a little bit more positive than they first thought. He's not fit to play for Leinster, so hopefully he is going to spend this week with us."

Dr. James Robson, the Lions' doctor, also put a positive spin on O'Brien's injury saying the flanker "is in better condition than we thought and he continues his recovery at pace."